No matter what I've tried I can't execute a coastal assault – ie, land an army from a ship and attack a castle in the same turn. Even if the castle is right there on the coast, the army always just disembarks from the ship, chills for a turn and only on the next turn can it actually do anything.
What's worse, I've seen the AI actually do this successfully – land and attack in the same turn. Are my generals missing something? Some trait or ability?
Best Answer
After some more testing, it seems that the AI lands and attacks in the same turn under one condition - that the castle is garrisoned with units (other than the automatic units spawned by the castle). On disembarking, the player is given a chance to intercept and then the AI attacks the castle in the same turn.
I haven't had the opportunity to test this further (can you refuse to intercept and thus force them to wait? can the player do the same thing?) but it seems like a really odd design choice - most castles in the rear (which is where, presumably, you're supposed to be doing the attacking) aren't garrisoned, thus making this almost completely useless.
Anyway, hope it helps somebody, it certainly had me stumped for a while.